Heavy metal-ions, such as hexavalent chromium (Cr(VI)), are extremely hazardous to humans, animals, and the environment and as such the World Health Organization (WHO) mandated a maximum allowable concentration of these heavy metal-ions in water, for example, 50 ppb for Cr(VI) in water. Heavy metal-ions are produced by a wide variety of processes used in industry. For example, in manufacturing, electroplating, textile, and tannery industries through the combustion of coal and oil or as part of the waste in the process.
As an example, wastewater from tanneries may contain Cr(VI) concentrations upwards of 3,500 ppm. The majority of industries, however, generate wastewaters with Cr(VI) concentrations up to 100 ppm. Adsorption is a commonly used method for treating water and wastewater streams containing heavy metal-ions, such as Cr(VI), and most adsorbents for heavy metal-ions, including Cr(VI), and other anions, rely on nitrogen-based functional groups. Industrially, synthetic polymers are often used rather than naturally occurring materials for adsorbing heavy-metal ions, including Cr(VI), due to their greater adsorption capacities. Production of synthetic polymer based adsorbents itself produces undesirable wastes such as increase in carbon footprint and other industrial wastes.
Therefore, there is a need for economic environmentally friendly biomass-based adsorbents for removing heavy metal-ions from a solution.